The relative importance of sea, conditions (state of the sea) versus 

 water temperature on the deterioration of an iceberg can only be 

 assumed until more studies are made. The sea state is important 

 to the erosion of the berg, especially near the water line, and 

 in setting up stresses and strains to cause calving of pieces or even 

 breaking-up of the berg. The deterioration of ice due to the water 

 temperature is more subtle. The rate of melting of the ice at its 

 underwater surface depends directly on the sea temperature. Differ- 

 ences in air and sea temperatures are probably important in setting 

 up stresses within the berg. Both factors are mutually dependent 

 in their overall affect on berg deterioration. The roughness of sea 

 conditions increases the melting effect by assisting in the exchange 

 of water around the berg. The ice-water temperature differential 

 assists the sea state in calving or breaking-up of bergs by setting up 

 stresses within it. There is no doubt that a given berg will survive 

 much longer in calm than in rough seas at a given water temperature. 

 Also the same berg will survive much longer under given sea condi- 

 tions at lower sea temperatures. Ordinarily the average sea conditions 

 on the Grand Banks for a given calendar period do not vary much 

 from year to year. At least it is believed that the effect on deteriora- 

 tion of ice from sea conditions is subject to less variation for given 

 calendar periods than from variations in sea temperatures. Thus 

 it is assumed that the sea water temperature, as represented by the 

 bimonthly isotherm chart, is a more important and more useful con- 

 sideration. To say the least, the bimonthly isotherm chart is a useful 

 tool in assessing the ice environment and forecasting ice deterioration. 

 The International Ice Patrol has recognized the importance of sea 

 water temperatures on the deterioration of ice ever since its inception 

 in 1913. Surface temperatures recorded by Ice Patrol vessels and 

 reporting ships have been plotted over the years. Isotherm charts 

 have been constructed for the periods of the patrols since 1919. Since 

 1951 isotherm charts based on numerous reported sea temperatures 

 have been drawn on a bimonthly basis during the ice season. Normal 

 bimonthly isotherm charts have been constructed for the interval 

 1951-63 during the Grand Banks ice season from mid-February 

 through June. See figures 45-53. While the bimonthly normals for 

 the periods from mid-March through May can be considered true 

 normals, the others, especially the 15-28 February chart, should not 

 be considered true normals. The Ice Patrol is not usually commenced 

 until early March unless abnormally bad ice conditions require ai) 

 earlier start. Thus the 15-28 February chart, which is based on only 

 3 years data, is more indicative of a 15-28 February environment 

 during hea\'y ice seasons and/or early ice seasons. The 1-15 March 

 chart is based on 6 years' data and somewhat more representative of 

 normal conditions, although it is pointed out that this chart probably 



35 



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